The present invention relates to a scanning radar system that transmits radio waves while scanning the projection direction thereof, that determines the lateral position of a target based on the strength of a reflected wave returned from the target and, more particularly, to a scanning radar system that measures the lateral position of a target as well as the distance and relative velocity thereof for vehicle-to-vehicle distance control.
A vehicle equipped with an FM-CW radar can measure the distance and relative velocity of a target located ahead of the vehicle. If the distance, for example, to a vehicle traveling ahead is to be properly controlled based on these measured values, the lateral position of the target located ahead must be determined.
A scanning radar system, as shown in FIG. 1(b), transmits a radiowave while scanning the projection direction thereof, and determines the lateral position of a target based on the direction in which the target is located, i.e., the direction in which the strength of the reflected wave from the target is the highest.
According to this method, the lateral position of the target can be determined accurately, provided that there is no displacement between the direction to which the target is located when viewed from the radar-equipped vehicle (the direction to the target) and the direction in which the target is traveling (the heading of the target).
However, if there is a displacement between the direction to the target and the heading of the target, the lateral position of the target cannot be determined accurately. For example, in the case shown in FIG. 1(a) or 1(c), as the power of the reflected wave is the highest at one edge of the target, the lateral position of the target cannot be estimated accurately.
Accordingly, it is an object of the present invention to provide a scanning radar system that can accurately determine the lateral position of a target even when the heading of the target is displaced from the direction to the target.
According to the present invention, there is provided a scanning radar system comprising: lateral position determining means for determining a lateral position X of a target, based on the strength of a reflected wave returned from the target when radio waves are projected while scanning the projection direction thereof; means for determining an angle xcexa8 between a direction to the target and a heading of the target; means for determining a correction value xcex94X for the lateral position based on the angle xcexa8; and means for correcting the lateral position X by the correction value xcex94X.
Preferably, the angle xcexa8 determining means determines the angle xcexa8, based on a turning radius R, a distance d to the target, and an angle xcex8 between the direction to the target and the heading of a vehicle equipped with the radar system, by calculating equation
xcexa8=xcex8xe2x88x92tanxe2x88x921{d cos xcex8/(Rxe2x88x92d sin xcex8)}